Climate changes such as global warming may be due to changes in the sun rather than to the release of greenhouse gases on Earth.
Climatologists and astronomers speaking at the American Association for the Advancement of Science meeting in Philadelphia say the present warming may be unusual - but a mini ice age could soon follow.
The sun provides all the energy that drives our climate, but it is not the constant star it might seem.
Careful studies over the last 20 years show that its overall brightness and energy output increases slightly as sunspot activity rises to the peak of its 11-year cycle.
And individual cycles can be more or less active.
The sun is currently at its most active for 300 years.
That, say scientists in Philadelphia, could be a more significant cause of global warming than the emissions of greenhouse gases that are most often blamed.
The researchers point out that much of the half-a-degree rise in global temperature over the last 120 years occurred before 1940 - earlier than the biggest rise in greenhouse gas emissions.
Ancient trees reveal most warm spells are caused by the sun
Using ancient tree rings, they show that 17 out of 19 warm spells in the last 10,000 years coincided with peaks in solar activity.
They have also studied other sun-like stars and found that they spend significant periods without sunspots at all, so perhaps cool spells should be feared more than global warming.
The scientists do not pretend they can explain everything, nor do they say that attempts to reduce greenhouse gas emissions should be abandoned. But they do feel that understanding of our nearest star must be increased if the climate is to be understood.
Understanding how the atmosphere works is fundamental to understanding climate change. The atmosphere is composed of layers of air, each with its own temperature patterns. Researchers must determine whether changes in temperature or air circulation are part of complex, longer-term cycles. And the interconnections between air, sea, and land mean that any change could have multiple causes—and multiple effects.
The Images below show a lot of interesting things - The change in the depth of Vostok Ice cores, Global Average Glacier Erosion, the dates of oak leafing in New England for the last 200+ years, A map of predicted and actual rainfall changes based on the climatic change model (very close predictions), and a map showing the greening of the Northern Hemisphere - but the most interesting graphic is the one which shows Solar activity against climate.
Space weather may also in the long term affect the Earth's climate. Solar ultra-violet, visible and heat radiation are the primary factors for the Earth's climate, including global average temperatures, and these energy sources appear to be quite constant. However, many scientists have observed corrrelations between the solar magnetic activity, which is reflected in the sunspot frequency, and climate parameters at the Earth. Sunspots has been recorded through several hundreds of years which makes it possible to compare their variable frequency to climate variations to the extent that reliable climatological records exists. One of the most striking comparisons was published by E. Friis-Christensen og K. Lassen, DMI, in "Science" in 1991. In their work they compared the average temperature at the northern hemisphere with the average solar activity defined through the interval between successive sunspot maxima. The more active the sun - the shorter the interval: the solar cycle runs more intense.
The red curve illustrates the solar activity, which is generally increasing through an interval of 100 years, since the cycle length has decreased from around 11.5 years to less than 10 years. Within the same interval the Earth's average temperature as indicated by the blue curve has increased by approximately 0.7 degree C. Even the finer structures in the two curves have similar appearances.
(Reference: Friis-Christensen, E., and K. Lassen, Length of the solar cycle: An indicator of solar activity closely associated with climate, Science, 254, 698-700, 1991).
So what does it all mean? Well, an increase in global Climate Temp may not mean it's hotter for everyone. For example, Continental Europe (and the UK) enjoy the weather they do because of the course of the Gulf Stream, an increase in global climate temp would make Europe Colder, not Warmer - West texas would become wetter and colder while places like Wisconsin would be drier and hotter; Global Warming doesn't mean everyplace all the time.
But, I'm liking the sun correlation, nice [relatively] clean data takes - and we Statisticians love clean sets... Makes for nicer Multi-Dimensional Sims.
Global warming: Real and Present Danger
Cause: UNKNOWN, further research required, too many factors.
Edited by Gefiltefishmon, 25 December 2004 - 08:03 PM.